Resilience Updates (#450)

1. Move the act of poping a job off of a queue to a transaction via watch and multi.

   • This will have speed implications. In a busy system, the occurrences of trying to "pop" while writes are happening is high.
   • We may want to move to a LUA implementation to be truly blocking

2. Add queue.retryStuckJobs() which is a single method to retry jobs which have failed due to the worker timeout.

3. Add options.retryStuckJobs to the Scheduler, to automatically run the above queue.retryStuckJobs() periodically.